Mosaic screen



May 1942. v s. F. ESSIG 2,282,123 2 MOSAIC SCREEN Q Filed Jan. 25; 1941 INVENTOR Patented May 5, 1942 MOSAIC SCREEN Sanford F. Essig, Fort Wayne, Ind., assignor to Farnsworth Television a corporation of Delaw and Radio Corporation, are

Application January 23, 1941, SerialNo. 375,660

4 Claims.

This invention relates to an improved mosaic of discrete particles and a method of producing the same, and more particularly relates to-a mosaic screen of discrete metallic particles suitable for use in cathode-ray tubes in television and similar apparatus.

In the past such mosaics have usually been made by producing a metallic film on a surface of an insulating or semi-conducting foundation and disrupting this film by heating. However, the manufacture of these mosaics by previously known methods either has required the use of excessively high temperatures resulting in injury to other parts of the tube employing the mosaic, or in the mosaics not being entirely satisfactory, due to the imperfect separation between the metallic particles with consequent leakage of electrical charges from certain particles to other adjacent particles.

It is an object of the present invention to provide an improved mosaic of the character above referred to.

A further object is to provide an improved method for producing mosaics requiring only moderate temperatures and rendering mosaics which are highly satisfactory in performance due to the distinct separation between the particles I thereof.

In accordance with the present invention, the method of producing a mosaic of discrete particles comprises the steps of applying a metallic film to a surface of a foundation, and subjecting the film to the vapor of a metal different from that of said film, thereby to lower its viscosity. The treated film is then heated to cause its disruption into discrete particles thereby producing the improved mosaic structure. In accordance with a further feature of the invention, the disrupted film is retained at an elevated temperature for a predetermined length of time in order to expel the metallic vapor from the disrupted film.

In accordance with a preferred embodiment of the present invention, a metallic film is produced on a surface of an insulating or semiconducting foundation plate in any suitable manner which provides thereon a substantially uniform film, as for example by evaporation or sputtering. This film is then exposed to an atmosphere of metallic vapor. As a consequence thereof, the metallic film changes its viscosity due to amalgamation with the metallic vapor. After the film has been treated in this manner, it is subjected to heat for the purpose of cansing its disruption into discrete metallic particles.

The fact that the metallic film is in the form of an amalgam greatly facilitates the formation of well-spaced particles of bead-like shape. The heating can be continued until practically all of the metallic vapor is expelled from the disrupted film, leaving substantially puremetallic particles.

For a better understanding of the invention, together with otherand further objects thereof, reference is made taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 illustrates the treatment of a metallic film in accordance with the present invention. while Fig. 2 shows a cross-section through the finished mosaic of discrete particles.

Referring now more particularly to Fig. 1 of the drawing there is shown in cross-section a thin metallic film I, preferably of silver, deposited by evaporation or sputtering on a foundation 2 of insulating material, such as mica, glass or the like. The foundation can also consist of semi-conducting material and is preferably resistive to the metallic vapor to which the film I is to be exposed. In the simplest manner in which this invention can be exercised, there is provided a receptacle 3 containing a pool of mercury 4, above which the film I is suspended and exposed to the mercury vapor emanating from the pool 4.

After a suflicient exposure of the film I to the mercury vapor, which is best determined experimentally, the film I together with its foundation 2 is subjected to a heat treatment as is conventional for disruption of thin metallic films into discrete particles. However, due to the previous exposure of the film to mercury vapor the temperature required for disruption is much lower than that hitherto necessary. In fact, temperatures-in the order of only 200 centigrades are only required, as compared with 800 centigrades generally employed; It will be obvious to those skilled in the art that the use of a much lower temperature is of great advantage since it permits the disruption of the film without endangering the foundation or elements of an electron discharge tube of which the film may be a art at the time of the heat treatment.

The disrupted film is preferably retained at an elevated temperature for a predetermined length of time. sufficient to expel the mercury vapor from the disrupted film and to obtain substantially pure metallic silver particles.

to the following description 2,282,128 I Fig. 2 shows a cross-section through the mosaic foundation, exposing said film to the vapor "of Y a of particles I on the foundation 2. The surfaces metal different from that of said film, and heatof the particles are then ready for oxidation and ing said film after exposure to said vapor to cause treatment with photosensitive material, such as its disruption into discrete particles. caesium, to produce a photosensitive mosaic 5 2. The method of producing a mosaic electrode screen of the type employed in television picture of discrete metallic particles, comprising the steps signal generating tubes. of producing a metallic film on a surface of a Examination by microscope of mosaic screens foundation, exposing said film to the vapor of a produced in accordance with the present invenmetal different from that of said film to lower tion indicates that the metallic particles of these its viscosity, heating said film after exposure to screens are substantially circular in configuration said vapor to cause its disruption into discrete and separated from each other by a distance particles, and retaining the disrupted film at an roughly corresponding to their diameters; It is elevated temperature for a predetermined length apparent, therefore, that such a screen is parof time for expulsion of said vapor from said disticularly well adapted for use in high-definition rupted film. television systems due to its low surface leakage, 3. The method of producing a mosaic electrode resulting in improved definition of the television of discrete metallic particles, comprising the steps pictures produced therein. of producing a metallic film on a surface of a While there has been described what is a foundation, exposing said film to mercury vapor present considered the preferred embodiment of 2 to lower its viscosity, and heating said film after the invention, it will be obvious to those skilled exposure to said vapor to cause its disruption into in the art that various changes and modifications discrete particles. may e therein o t departing from the 4. The method of producing a mosaic electrode i e and it therefore. aimed 1n the P- of discrete silver particles, comprising the steps pended claims to cover all such changes and of producing a ilv r mm on a, surface. of a modifications as fall within the true spirit and foundation esistiv to mercury vapor, xposing scope of the invention. said film to mercury vapor to lower is viscosity, What is claimed is: and heating said film after exposure to said vapor 1. The method of producing a mosaic electrode to cause its disruption into discrete particles. of discrete metallic particles, comprising the steps of producing a metallic film on a surface of a SANFORD- F. ESSIG. 

